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This study is based on simulation with this GM model, where the beam line elements (i.e. magnets etc.) are displaced with respect to the first element by the GM model. The GM along the beam line is measured by a number of Guralp seismometers with the transfer function (TF). So, the GM is corrected by the TF. On-line, only the real part can be corrected ( feed-forward implementation). The tracking code is PLACET. Also, incoming beam jitter ( 6Hz, 100 pulses), BPM noise and sensor TF are included. In this study, all sextupoles are turned off.
First, sensitive elements are identified by making matrices of the GM effect in a plane of elements and the BPMs. The high sensitive elements are selected to have GM sensors. First and last elements have the sensors. Since the number of sensors are limited to 15, 20 and 30, displacements due to the GM of other elements are estimated by linear interpolation.
Next, the GM induced beam displacements are estimated by the 15, 20 or 30 sensors and the estimated ones are subtracted from BPM readings. The 15 sensors are not enough for the estimation, especially in horizontal direction. The 30 sensors are the most preferable for the estimation.
Actually, the incoming jitter exceeds the GM effect by about 100 times. The simulation shows very good removal/correction of the incoming jitter, where the incoming x, x', y, y' and ΔE/E are reconstructed in pulse by pulse and propagated along the beam line. The 20 and 30 sensors have good correlation between the displacements corrected jitter and the GM effect, especially in vertical direction.
Proposed feed-forward aims to correct the GM effects in next pulse with the GM measurements on quadrupoles between the pulses, e.g. 6Hz in this simulation. The principle would be demonstrated at ATF2 for the BPM systems with 100nm resolution and um level reconstruction which have been achieved, if there are sensors and fast-enough correctors.
Open questions are listed below.
The electronics block diagram was shown, where all the signals of reference cavities and IPBPM-cavities in the c-band are down-converted to 714MHz, then the IPBPM converted signals are detected with respect to the reference ones ( outputs from the limiter) . The detected signals with 2 phases, i.e. I and Q, are digitized by the 14bit ADC. The reference signals are also digitized in the ADC for the beam intensity. The converter and combiner of the IPBPM signals are located close to the IPBPMs, while the detector and ADC are put in the Eel's bedroom (DAQ room).
The electronics noise determining the minimum position resolution comes from the first amplifier in the converter. Therefore, the sensitivity/linearity of the converter was measured at the test bench. The output powers (714MHz) were measured to be linear down to the input power of about -120dBm ( 5.712GHz in X, 6.426HHz in Y). Since the 1nm input power is about -100 dBm, the basic performance was verified.
For high resolution study, the mechanical support must have good coherence between the IPBPM blocks. Vibrations were measured with 2 different supports, i.e two post mover and SLAC mover in 2011.2.9 (Wed.) in the tunnel and 2011.3.4 (Fri.) outside of the tunnel, respectively, both with Sugahara-san. Six accelerometers ( sensitive from 0.1 to 100Hz ) were put on the floor, table and IPBPMs. The SLAC mover system was chosen for better performance on the coherence especially in Y.
The IPBPM system will be installed on a granite table at the upstream test area in this summer. There is a switchable beam line so that it will on the beam line only for the beam test.
There are electronics for 3 IPBPM cavities. So, we need one more electronics. Also, we need an adapter plate between the SLAC mover and the granite table for the switchable beam line, mover controller and the Helix cables from inside of tunnel to eel's bed room, too. We will check the electronics and digitizer.
We checked purity, i.e. it is OK. The filter works well.
It happened again, when we added the cooling water for shortage, i.e. the laser stopped. The purity seems OK. But, the water temperature was high, 30oC since the box stored water is outside the laser room. If this is the reason, laser should recover by itself. Then, this morning, the laser started. We do not know if the temperature was too high, or air bubbles disturbed flow sensor .
We will store water inside laser room, and refill some time ahead of beam time. However, we need to investigate all possibilities.
Next, Oroku briefly reported that the status monitor of IPBSM will be updated for any shift members before this autumn beam run. There are 86 parameters to be monitored in 2 display panels at both the control and DAQ rooms. The panels show that the green status is OK, while the red one is to ask you for calling an IPBSM member.
Next meeting is 13th July, 2011.